The purpose of this study is to investigate the incidence of os acromiale in patients who had reverse shoulder arthroplasty (RSA) for rotator cuff tear arthropathy and the effect of presence of os acromiale on the functional results.

We hypothesize than in the presence of os acromiale, the contraction strength of the deltoid would decrease due to the dynamic downward depression of the bony fragment leading to less favorable clinical results.

A total 46 patients with a mean age of 70.8 who had RSA and a minimum follow-up of 24 months were included in this study. Preoperative radiographs, computerized tomography scans and magnetic resonance images were examined to determine the presence of os acromiale.

A total of 10 patients out of 46 (22%) with os acromiale, all of which were of mesoacromion type, were followed up for 59.7 months. While both groups had significant improvements in Constant, Q-DASH and VAS scores compared to their preoperative status, a significant difference between the groups could not be found. The radiological evaluation showed that the average acromiohumeral distance significantly increased postoperatively in both groups. The acromiohumeral distance was significantly shorter in patients with os acromiale.

While the presence of os acromiale does not have an adverse effect on the clinical results of the RSA, the loose fragment can migrate distally in the postoperative period due to the tension in the deltoid.

III, case-control study.